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Given the price of Di2 wiring bits
As against the price of a solder station, a hot airgun, some adhesive lined heat shrink, your own time and the downtime every time a solder connection dies from vibration? I'm all for being a hacker, but in most cases is strictly for the lols because the mass produced solution is actually cheaper.
gbj_tester-
Pretty sure the number of folks who'd contemplate rolling their own loom, who don't already have the necessary kit, would be damn close to zero. Dropping a grand and a half on derailers, shifters and an A junction and battery left me rather reluctant to blow any more dough; in my case DIY was totally worth the time, and it was also fun.
In addition to tinkering tightarses, full-on gram-chasing weight weenies might also be tempted, given it's a tad lighter.
And it's a bike, not a 20t hydraulic hammer. Your soldering skills must blow chunks if you'd be worried about vibration.
Speaking of, my loom is made from single-insulated wires (probably Teflon, judging from how annoying it was to strip) harvested from better-quality USB cables, plaited with fuzzy twine, and that trick has been successful in preventing any buzzing or rattles.
Kimmo
Given the price of Di2 wiring bits, I'm surprised I'm the only one I know of who only bought the minimum number of EW-50s to get plugs for levers and derailers... It's just wire. Pretty damn fancy wire, but it doesn't need to be anywhere near that tough, and waterproofing isn't rocket surgery. The B junction doesn't do anything a couple of blobs of solder can't...